A typical commercial available Liquid Crystal Display (“LCD”) as shown in FIG. 6 uses one or more fluorescent lamps 601 as its light source. A light guide 603 projects light from these fluorescent lamps 601 through the LCD screen based on the principle of total internal reflection. Typically, a wedged light guide is used when the lamp or lamps are located only at one side of the display and a parallel light guide is used when the lamps are located at two opposite sides of the display. Usually, there is also one or multiple driver boards 705 (see FIG. 7) located behind the light guide to control the operation of the LCD.
High powered Light Emitting Diodes (“LEDs”—for example Luxeon 1, 3 and 5 watt LEDs manufactured by Lumileds) are available for a backlight for sunlight readable LCD. With energy efficiency over 20 lumens per watt, these LEDs can provide more than a hundred of lumens of light output from a compact package. Because these LEDs have a very high power density, a significant amount of heat is generated. Thermal management becomes one of the most critical factors in LED source design.
Typically, the above mentioned LED has an anode and a cathode lead spreading horizontally for conducting electrical current in or out from the device as well as a metallic bottom slug for heat transfer. Conventionally, the LED is soldered to a metal core printed circuit board, which is parallel to the bottom surface of the metallic slug of the LED. The printed circuit board is then bonded to a large heat sink. Since there is a printed circuit board between the LED and the heat sink, the overall thermal resistance is increased. The cost of the metal core printed circuit board is high, and the width of the final assembly is wider than the total width of the LED.
Night Vision Image Systems (“NVIS”) that are compatible with such sunlight readable LCDs are also known in the art. Normally, in order to combine a sunlight (or daylight) readable LCD with a NVIS, existing fluorescent lamps and light guides associated with a commercial off-the-shelf LCD display are removed, and replaced with a diffuser and an array of LEDs. In many cases, the LCD driver board must be relocated to make room for the LED array. Such an approach requires significant repackaging work and adds considerable cost to the display manufacturing process. Furthermore, internal cooling fans or heat sinks are required to remove the heat generated by the LED array. This also increases the depth and bulk of the display.